Imaging system and driving method thereof

ABSTRACT

When a gain correction is performed for the radiographed object image, the acquisition of the object image having a high grade quality and no artifact is realized. For that purpose, an image storing unit is provided for storing an image for correction radiographed based on conditions set with the table in a state in which no object exists to each operation modes of the plurality of operation modes; and an image processing unit is provided for performing a gain correction processing of the radiographed object image and performs the gain correction processing of the radiographed object image obtained based on the conditions set in the table of the operation mode selected by the selecting unit in a state in which the object exists using a corresponding image for correction extracted from the image storage unit based on the operation mode selected by the selecting unit.

RELATED APPLICATIONS

This is a divisional of application Ser. No. 12/328,302, filed Dec. 4,2008, which is a divisional of application Ser. No. 11/751,686, filedMay 22, 2007 (now U.S. Pat. No. 7,476,027, issued Jan. 13, 2009), claimsbenefit of both of those applications under 35 U.S.C. §120, and claimsbenefit under 35 U.S.C. §119 of Japanese patent application no.2006/167876, filed Jun. 16, 2006. The entire contents of each of thethree mentioned prior applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation imaging system forradiographing a radiation image of an object and a driving methodthereof.

2. Description of the Related Art

In general, a demand for digitalization of an x-ray image in thehospital has been recently increasing. In reality, a radiation imagingapparatus such as, for example, FPD (Flat Panel Detector) has began tobe used, in which an x-ray dosage is converted into electric signals byusing a solid state imaging device in which x-ray detection elements(conversion elements) are disposed in a two-dimensional array patterninstead of a film.

In this X-ray imaging apparatus, since an X-ray image can be replaced bydigital information, the image information can be transferred far awayand instantaneously and this provides the advantage of being able toreceive a sophisticated diagnosis comparable to a university hospital inthe heart of the city, while being far away. Further, there is also theadvantage of being able to save a storing space of the film in thehospital in case the film is not used. In future, if an excellent imageprocessing technology can be introduced, an automatic diagnosis using acomputer without an intermediary of a radiologist can be expected withgreat hopes.

In recent years, a radiation imaging apparatus has been put to practicaluse, in which an amorphous silicon thin film semiconductor is used forthe solid state imaging device so as to radiograph a static image.Specifically, by using the manufacturing technology of the amorphoussilicon thin film semiconductor, the radiation imaging apparatuscomprising a solid state imaging device enlarged in its area exceeding40 cm square to cover the size of human chest regions has been realized.This radiation imaging apparatus, because of relative easiness of itsmanufacturing process, is expected to provide an inexpensive apparatusin future. Moreover, since the amorphous silicon can be manufactured ona thin glass plate below 1 mm, it has an advantage of being able to makethe thickness extremely thin as a detector. Such a radiation imagingapparatus, for example, is disclosed in Japanese Patent ApplicationLaid-Open No. H08-116044.

Further, more recently, development of radiographing a moving image isunderway in such a radiation imaging apparatus. If such a radiationimaging apparatus can be manufactured at a moderate price, the stillimage and moving image can be radiographed by the same one set, so thatpopularization of the apparatus can be expected in many hospitals.

SUMMARY OF THE INVENTION

When a moving image is radiographed by using the radiation imagingapparatus, as compared to the still image, the shortening of read time(quickening a frame rate) and the improvement of a S/N cause a problem.Hence, when the moving image is radiographed, a driving generallyreferred to as <pixel addition> is performed. Usually, a single pixel isread as one pixel (hereinafter, this one pixel is referred to as <unitpixel>), whereas, in the pixel addition, a plurality of pixels is puttogether and read as one pixel (hereinafter, this one pixel is referredto as <plural pixel>).

Next, by using circuit diagrams shown in FIGS. 11 and 12, the pixeladdition will be described.

A technique for the pixel addition is variously considered. For example,this includes a technique in which two pieces of gate wiring are turnedon at the same time, and as shown in FIG. 11, an analogue signal issubjected to the pixel addition before the AD conversion of an ADconverter, and a technique in which, as shown in FIG. 12, the digitalsignal is added after the AD conversion. In the case of the former,since the analogue signal is added, and after that, the A/D conversionis performed, the data amount for the AD conversion is reduced, and theread time can be shortened. In contrast to this, in the case of thelater, since the analogue signals are all AD-converted into digitalsignals, and then, the digital signals are added, the read time takeslong. Further, as compared to the addition of the digital signals, theaddition of the analogue signals is small in noise and high in S/N.

A quantum noise of the X-ray shown in FIGS. 11 and 12 is taken as<X-RAY>, and a shot noise of dark current of the conversion element istaken as <Senser>. Further, when a noise of a readout circuit unit (AMP)shown in FIGS. 11 and 12 is taken as <AMP> and a noise of the ADconverter as <AD>, a total of noises can be determined by a sum ofsquares.

Specifically, the total noises by the analogue addition of FIG. 11 areshown by the following formula. 4×4·Analogue addition noise=√{(2X-RAY)²+(2Senser)²+(AMP)²+(AD)²}

As shown in the above described formula, in the case of the analogueaddition, the quantum noise <X-RAY> of the X-Ray and the noise <Senser>of the conversion element become (√2 times).

Further, a total of noises by the digital addition of FIG. 12 are shownby the following formula.·Digital addition noise=√{(2X-RAY)²+(2Senser)²+(2AMP)²+(2AD)²}.

As shown in the above described formula, in the case of the digitaladdition, all the noises become (√2) times, and as compared to the casewhere the analogue signal is added, the noise becomes large.

Further, since an amount of the signal becomes twofold both for theanalogue addition and the digital addition, the digital addition ratherthan the analogue addition has the S/N reduced.

Hence, the pixel addition is quick in frame rate, and the pixel additionhaving an analogue signal high in S/N is generally performed. Further,the pixel addition can perform radiographing by changing the number ofpixels by the addition of a total of four pixels (hereinafter, two×twopixels addition) of two pixels in the direction to the gate wiring andtwo pixels in the direction to the signal wiring and a total of ninepixels of three pixels in the direction to the gate wiring and threepixels in the direction to the signal wiring.

More increased the number of pixels is, more shorter the read timebecomes, and the frame rate and the S/N are improved, whereas theresolution is deteriorated since a plurality of pixels is put togetherinto one pixel and output as one pixel (plural pixels). Hence, in viewof the frame rate, S/N, and resolving power, the engineer who performsthe radiographing selects the pixels according to the state of theobject.

Further, the radiation imaging apparatus performs a gain correction(sensitivity correction) since there exist irregularities of thesensitivity of the conversion element such as a photoelectric conversionelement and gain irregularities of Amps A1 to A4. The gain correction isperformed such that an X-ray is irradiated and radiographing isperformed in a state in which no object exists in advance, and theobtained image for gain correction is kept in a memory, and when anobject is radiographed, the object image is divided by the image forgain correction. This image for gain correction, because of the timeaging also of the conversion element, is periodically renewed by theengineer who uses the same. This renewal operation is referred to as<calibration>.

Further, since the image actually diagnosed by the doctor is an imagesubsequent to the gain correction performed to divide the object imageby the image for gain correction, both the S/N of the object image andthe S/N of the image for gain correction affect the image. Hence, whenthe S/N of one image is low, the S/N of the image after correction isreduced. From this, it is clear that, when the pixel addition isperformed, the image for gain correction had better to use the imageadded with the analogue signals and having a high S/N, and in theradiation imaging apparatus having a plurality of radiographing modesdifferent in the number of pixel additions, it is preferable that theimage for gain correction is available every radiographing mode.

For example, when the object image is added with the analogue signals of2×2 pixels and is radiographed, the image for gain correction added withthe analogue signals of 2×2 pixels and radiographed is used. Further,when the object image is added with the analogue signals of 3×3 pixelsand is radiographed, the image for gain correction added with theanalogue signals of 3×3 pixels and radiographed is used. Further, in thecase of the 2×2 pixel addition or the 3×3 pixel addition, a sum total ofthe number of pixels is increased by a total of four pixels or a totalof nine pixels, and so when the same dosage as the X-ray not subjectedto the pixel addition is irradiated, the signal output is also increasedby four times or nine times, respectively. Hence, the dynamic range ofthe read circuit (Amp) or the AD converter ends up being saturated, anda normal signal is not output. That is, in this case, there arises aproblem that acquisition of a high quality radiographed image becomesdifficult.

Next, by using FIGS. 13A to 13D, an artifact caused when the objectimage and the image for gain correction are radiographed by differenttube voltages will be described.

The radiation imaging apparatus, as shown in FIG. 13A, is configured tobe laminated with phosphors on photoelectric conversion elementstwo-dimensionally disposed, and forms a conversion element. The phosphorconverts an incident X-ray into a visible light, and converts thevisible light into an electric signal by the photoelectric conversionelement. The phosphor, while a material composed primarily of CsI andGOS is used, mainly uses CsI of columnar crystal excellent in DQE andMTF. This CsI is formed by a method referred to as vacuum evaporation,and generates an irregularly shaped defect as shown in FIG. 13A, whichis referred to as splash. This splash is inevitably generated when CsIis vacuum-evaporated, and its complete elimination is difficult.

FIGS. 13B to 13D represent the outputs of the photoelectric conversionelement of the splash defect bottom of phosphor. The splash defectportion, as compared to other normal portions, is different in filmthickness of CsI, and thus different from the normal portion in theoutput to the tube voltage, and further, an absorbed dosage of the X-rayis different also by the tube voltage to be radiographed, therebygenerating the output change of the photoelectric conversion element.

For example, as shown in FIG. 13B, when the tube voltage of the X-ray is80 kVp, the output of the photoelectric conversion element is reduced byapproximately 20% as compared to the normal portion, whereas, as shownin FIG. 13C, when the tube voltage is 60 kVp, the output of thephotoelectric conversion element is reduced by approximately 10% ascompared to the normal portion. Hence, for example, when the objectimage is radiographed by the tube voltage 60 kVp, and the image for gaincorrection is radiographed by the tube voltage 80 kVp, if the divisionof the object image by the image for gain correction is performed, thegain correction of the splash defect is unable to be performed, and thisends up emerging as a reduction of 12% as shown in FIG. 13D.Hereinafter, the gain correction performed by using the radiographedimages in this manner by the different tube voltages is referred to as<different tube voltage gain correction>.

The error due to such a gain correction becomes a cause of a falsediagnosis by the doctor. Such a gain corrector error happens not only toCsI, but also to phosphor of GOS, amorphous selenium that converts theX-ray directly into an electric signal without using phosphor, galliumarsenide, mercuric iodide, and the conversion element using lead iodide,thereby creating a problem in that an artifact is generated on theradiographed image.

The present invention has been carried out in view of the abovedescribed problem, and an object of the invention is to provide aradiation imaging apparatus that realizes acquisition of an object imagehaving a high quality and no artifact when performing a gain correctionfor the radiographed object image.

The radiation imaging system of the present invention comprises: aradiation imaging unit for performing a radiographing of the radiationirradiated from a radiation generator for generating the radiation; atable storing unit for storing a table set with radiation conditions ofthe radiation of the radiation generator unit and driving conditions ofthe radiation imaging unit to each operation modes of the plurality ofoperation modes selected by a selecting unit for selecting an operationmode for performing a radiographing from among the plurality ofoperation modes; an image storing unit for storing an image forcorrection radiographed based on the conditions set with the table in astate in which no object exists to each operation modes of the pluralityof operation modes; and an image processing unit for performing a gaincorrection processing of the radiographed object image, wherein, theimage processing unit is performing the gain correction processing ofthe radiographed object image obtained based on the conditions set inthe table of the operation mode selected by the selecting unit in astate in which the object exists using a corresponding image forcorrection extracted from the image storage unit based on the operationmode selected by the selecting unit. A driving method of the radiationimaging system of the present invention is a driving method of theradiation imaging system comprising: a radiation imaging unit forperforming a radiographing of the radiation irradiated from a radiationgenerator unit for generating radiation and irradiating the sameoutside; and a table storage unit for storing a table set with anirradiation condition of the radiation of the radiation generator unitand a driving condition of the radiation imaging unit every eachoperation mode of the plurality of operation modes selected at aselecting unit for selecting an operation mode for performing theradiographing from among the plurality of operation modes; the drivingmethod of the radiation imaging system further comprising: a storingstep of storing the image for correction radiographed based on thecondition set in the table in the image storage unit in a state in whichno object exists every each operation mode of the plurality of operationmodes; an extraction step of extracting the corresponding image forcorrection from the image storage unit based on the operation modeselected by the selecting unit; and an image processing step ofperforming the gain correction processing of the object imageradiographed based on the conditions set in the table of the operationmode selected by the selecting unit in a state in which the objectexists by using the image for correction extracted by the extractionstep.

According to the present invention, when a gain correction is performedfor the radiographed object image, an object image having a high qualityand no artifact can be obtained.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration view of an x-ray imaging systemaccording to a first embodiment.

FIG. 2 which is composed of FIGS. 2A and 2B are equivalent circuitdiagrams showing a detailed configuration in an x-ray imaging apparatusof the x-ray imaging system according to the first embodiment.

FIG. 3 is a view showing one example of a calibration table used for thex-ray imaging system according to the first embodiment.

FIG. 4 is a timing chart showing a driving method in a non-pixeladdition of the x-ray imaging system according to the first embodiment;

FIG. 5 is a timing chart showing a driving method in a 2×2 pixeladdition of the x-ray imaging system according to the first embodiment.

FIG. 6 is a timing chart showing the driving method in a 4×4 pixeladdition of the x-ray imaging system according to the first embodiment.

FIG. 7 is a flowchart showing an acquisition processing of an image forgain correction of the x-ray imaging system according to the firstembodiment.

FIG. 8 is a flowchart showing the processing in the radiographingoperation of the x-ray imaging system according to the first embodiment.

FIG. 9 is a flowchart showing the acquisition processing of the imagefor gain correction of the x-ray imaging system according to a secondembodiment.

FIG. 10 is a view showing one example of a calibration table used forthe x-ray imaging system according to a third embodiment.

FIG. 11 is a schematic configuration view of a radiation imagingapparatus (x-ray imaging apparatus) used when an analogue signal issubjected to a pixel addition.

FIG. 12 is a schematic configuration view of a radiation imagingapparatus (x-ray imaging apparatus) used when a digital signal issubjected to a pixel addition.

FIGS. 13A, 13B, 13C and 13D are views for describing an artifact.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, preferable embodiments of the present invention will bedescribed in detail with reference to the drawings. Incidentally, invarious embodiments of the present invention, while the embodiment usingan x-ray as a radiation will be illustrated, the present invention isnot limited to this x-ray, and for example, α-ray, β-ray, γ-ray, and thelike should be construed as included also in the category of theradiation.

(First Embodiment)

FIG. 1 is a schematic configuration view of an x-ray imaging systemaccording to a first embodiment. As shown in FIG. 1, the radiationimaging system of the present embodiment is configured by being dividedinto an x-ray room 301 and an x-ray control room 302. In the x-ray room301 are placed an x-ray imaging apparatus 101 and an x-ray generatorapparatus 102. Further, a control apparatus 109 for controlling thex-ray imaging apparatus 101 and the x-ray generator apparatus 102 isplaced in the x-ray control room 302, and an engineer 110 is configuredto control the x-ray imaging apparatus 101 and the x-ray generatorapparatus 102 from the x-ray control room 102.

The engineer 110 performs a control for the x-ray imaging apparatus 101and the x-ray generator apparatus 102 through an operator interface 108.This operator interface 108 comprises a touch panel on a display, mouse,keyboard, joystick, foot switch, and the like. The engineer 110 can setirradiation conditions of the x-ray generator apparatus 102 such as atube voltage, tube current, irradiation time, and pulse irradiationmode, and driving conditions of the x-ray imaging apparatus 101 such asa radiographing mode (still image mode, moving image mode, and the like)and a radiographing timing by the operator interface 108. Further, theengineer 110 can perform a setting of various pieces of information onan image processing condition, an object ID, and a processing method ofthe captured image by the operator interface 108. However, since nearlyall pieces of the information are transferred from a radiationinformation system (not illustrated), there is no need to input themindividually. The important operation of the engineer 110 is aconfirmatory operation of the radiographed image. That is, the engineerperforms judgment as to whether or not its angle is correct, an object116 such as a patient moves, and an image processing is appropriate.

A radiographing controller 122 drives the x-ray generator apparatus 102serving as a radiation source and the x-ray imaging apparatus 101 fromthe radiographing conditions based on the instruction of the engineer110 or the radiation information system (not illustrated), and performsa control to capture image data. The radiographing controller 122transfers the image data captured from the x-ray imaging apparatus 101to an image processing unit 105, and after that, allows the imageprocessing designated by the engineer 110 to be performed by the imageprocessing unit 105, and allows this processing to be displayed on theoperator interface 108. At the same time, the radiographing controller122 allows the image processing unit 105 to perform a basic imageprocessing such as a gain correction, offset correction, whitecorrection, and defect correction, and stores the image data after theprocessing in an external storage unit 111.

Next, along with the flow of signals, the configuration and operation ofthe radiation imaging system of the present embodiment will bedescribed.

The x-ray generator apparatus 102 comprises a high voltage generatingsource 112, x-ray tube bulb 113, and x-ray aperture 114.

The x-ray tube bulb 113 is driven by the high voltage generating source112 controlled by the radiographing controller 122, and radiates anx-ray beam 115. The x-ray aperture 114 is driven by the radiographingcontroller 122, and accompanied with the change of radiographing areas,shapes the x-ray beam 115 so as not to perform unnecessary x-rayirradiation. The x-ray beam 115 is pointed at an object 116 lying downon an x-ray permeable bed for radiographing (not illustrated). This bedfor radiographing is driven based on the instruction from theradiographing controller 122. The x-ray beam 115 is transmitted throughthe object 116 and the bed for radiographing (not illustrated), andafter that, enters the x-ray imaging apparatus 101.

The x-ray imaging apparatus 101 comprises a grid 117, wavelengthconverter 118, x-ray exposure monitor 119, photoelectric conversioncircuit unit 120, and external circuit unit 121.

The grid 117 reduces the effect of an x-ray scattering generated by thetransmission of the x-ray through the object 116. This grid 117comprises an x-ray low absorbing member and an x-ray high absorbingmember, and, for example, is stripe-structured by Al and Pb. Theradiographing controller 122, at the time of the x-ray irradiation,vibrates the grid 117 so that moire is not generated by the relationshipof a grid ratio between the photoelectric conversion circuit unit 120and the grid 117.

The wavelength converter 118 includes phosphor comprising one kindselected from among Gd₂O₂S, Gd₂O₃, CaWO₄, CdWO₄, CsI, and ZnS as primarymaterial. The wavelength converter 118 has the main ingredient of itsphosphor excited by incident x-ray of high energy, and outputsfluorescent radiation of the visible area by recombination energy whenrecombined. The fluorescent radiation is based on per se main ingredientsuch as Gd₂O₃, Gd₂O₂S, CaWO₄, and CdWO₄, or based on the fluorescecenter substance activated inside the main ingredient such as CsI:Ti andZnS:Ag. Adjacent to this wavelength converter 118, the conversioncircuit unit 120 is disposed.

The conversion circuit unit 120 subjects a radiation towavelength-conversion to light by the wavelength converter 118, andconverts a photon of the light subjected to the wavelength conversioninto an electric signal. That is, the conversion circuit unit 120radiographs the radiation image of the object 116. Further, in theconversion circuit unit 120 is disposed each pixel (unit pixel)including the photoelectric conversion element (radiographing element)in a two-dimensional procession (two-dimensional matrix). In each pixel,a conversion element for converting the radiation into a charge includesthe wavelength converter 118 and the photoelectric conversion element.

The x-ray exposure monitor 119 is for monitoring the amount of an x-raytransmission. The x-ray exposure monitor 119 may directly detect thex-ray by using a light receiving element of crystal silicon and the likeor may detect a light from the wavelength converter 118. In the presentembodiment, a visible light (light in proportion to the x-ray dosage)transmitted through the conversion circuit unit 120 is detected by anamorphous silicon light receiving element of the x-ray exposure monitor119 which is deposited on a rear surface of the substrate having theconversion circuit unit 120 formed thereon, and this information istransmitted to the radiographing controller 122. The radiographingcontroller 122, based on the information from the x-ray exposure monitor119, drives the high voltage generating source 112 so as to shut off oradjust the x-ray.

The external circuit unit 121 comprises a driving circuit unit fordriving the conversion circuit unit 120, a readout circuit unit forreading a signal from each pixel of the photoelectric conversion circuitunit 120, and a power source circuit unit. This external circuit unit145 drives the conversion circuit unit 120 under a control of theradiographing controller 122, and reads the signal from each pixel, andoutputs it to the control apparatus 109 of the x-ray control room 302 asan image signal (image data).

The control apparatus 109 comprises the image processing unit 105,calibration table memory 106, image memory for gain correction 107,operator interface 108, external storage unit 111, and radiographingcontroller 122.

The image signal output from the x-ray imaging apparatus 101 istransferred from the x-ray room 301 to the image processing unit 105 inthe x-ray control room 302. At this transfer time, since the noiseaccompanied with the x-ray generation is loud inside the x-ray room 301,there is a possibility that the image signal (image data) is sometimesnot accurately transferred because of the noise. Hence, the increase ofnoise resistance of the transfer route is required. For example, thetransfer route is preferably provided with an error correction functionor otherwise uses a pair twisting wire with shield or an optical fiberby differential driver.

The image processing unit 105, based on the instruction from theradiographing controller 122, switches over the display data. Further,the image processing unit 105 performs various types of correctionprocessing such as an offset correction, gain correction and defectcorrection for the image data, and also a space filtering processing,recursive processing, and the like in real time. Further, the imageprocessing unit 105 performs a gradation processing, scattered radiationcorrection processing, spatial frequency processings of various types,and the like as occasion demands. Incidentally, in the presentembodiment, while the image processing unit 105 is provided outside ofthe x-ray imaging apparatus 101, it may be provided inside the radiationimaging apparatus 101.

The image data processed by the image processing unit 105 is displayedon the operator interface 108 as an image. Further, at the same timewith the real time image processing, the basic image data subjected tothe image data correction processing only is stored in an externalstorage unit 111. This external storage unit 111 is preferably a datastorage unit which is high-volume and high speed and satisfies highreliability, and for example, a hard disc array such as RAID ispreferable. Further, based on the instruction from the operator(engineer 110), the image data stored in the external storage unit 111is stored in another external storage unit. At this time, the image datais re-configured so as to satisfy the predetermined standard (forexample, IS&C), and after that, it is stored in another external storageunit. Other external storage units, for example, include a magneticoptical disc and a hard disc inside a file server on LAN and the like.

In the calibration table memory 106 is stored a calibration tableprovided with the driving condition of the x-ray imaging apparatus 101in each operation mode of the x-ray imaging system and the irradiationconditions of the x-ray of the x-ray generator apparatus 102. In theimage memory for gain correction 107 is stored each image data for gaincorrection radiographed in a state in which the object 116 does notexist for each operation mode of the x-ray imaging system. Incidentally,in the present embodiment, while the calibration table memory 106 andthe image memory for gain correction 107 are provided outside of thex-ray imaging apparatus 101, they may be provided inside the radiationimaging apparatus 101.

The x-ray imaging system of the present embodiment can be also connectedto the LAN through a LAN board, and is configured to have datacompatibility with HIS. This LAN is connected with a monitor fordisplaying still images or moving images, file server for filing theimage data, image printer for outputting the image on a film, imageprocessing terminal for performing complex image processing anddiagnostic support, and the like. Incidentally, it goes without sayingthat this LAN is connected with a plurality of x-ray imaging systems.Further, the x-ray imaging system in the present embodiment outputs theimage data according to the predetermined protocol (for example, DICOM).In addition, by using a monitor which is connected to the LAN, a realtime remote diagnosis by the doctor can be performed at the x-rayimaging time.

Next, the x-ray imaging apparatus 101 will be described in detail. FIGS.2A and 2B are equal circuit diagrams showing a detailed configuration inthe x-ray imaging apparatus 101 of the x-ray imaging system according tothe first embodiment. Here, in FIGS. 2A and 2B, from among eachcomponent part comprising the radiation imaging apparatus 101, theconversion circuit unit 120, driving circuit unit 121 a provided in theexternal circuit unit 121, readout circuit unit 121 b, and power sourcecircuit unit 121 c are shown. The conversion circuit unit 120, drivingcircuit unit 121 a, readout circuit unit 121 b, and power source circuitunit 121 c shown in these FIGS. 2A and 2B are, for example, composed byusing amorphous silicon thin film semiconductor.

This x-ray imaging apparatus 101, based on a control from theradiographing controller 122, is configured to be able to be driven inoperation modes of various types including a moving image radiographingmode and a still image radiographing mode.

In the conversion circuit unit 120 of FIGS. 2A and 2B are disposedpixels (unit pixels) 100 in a two-dimensional matrix pattern, whichcomprise one piece each of photoelectric conversion elements S1-1 toS8-8 comprising the conversion elements for converting the radiationinto the electric signals (electric charges) and switch elements T1-1 toT8-8 for capturing (transferring) electric signals from thephotoelectric conversion elements. In FIGS. 2A and 2B, for convenience,a total of 64 pieces of the unit pixels of eight pixels×eight pixels isshown.

Each unit pixel 100 of this conversion circuit unit 120, for example, isformed by using amorphous silicon thin film semiconductor on aninsulating substrate such as glass. Further, the photoelectricconversion elements S1-1 to S8-8 are formed by a MIS type structure or aPIN type structure with amorphous silicon taken as primary material. Inthis case, on the photoelectric conversion elements S1-1 to S8-8,wavelength converters 118 for converting the radiation into a light ofthe detectable wavelength area by the photoelectric conversion elementsare provided, and the photoelectric conversion elements are incidentwith a visible light from the wavelength converters 118. Incidentally,the photoelectrical conversion elements S1-1 to S8-8 may absorb incidentradiation (x-ray) and directly convert it into the electric charge. Thephotoelectric conversion element of the direct type, for example, takesone kind selected from amorphous selenium, gallium arsenide, mercuriciodide, lead iodide, and cadmium telluride as primary material. Further,as the switch elements T1-1 to T8-8, a TFT (Thin Film Transistor) formedby amorphous silicon on the insulating substrate such as glass can besuitably used.

The photoelectric conversion elements S1-1 to S8-8, for example,comprise photo diodes, which are reverse-biased. That is, a cathodeelectrode side of the photo diode is biased to + (plus). A bias wiringVs is a common wiring for supplying a bias (Vs) to each photo diode, andis connected to the power source circuit unit 121 c.

The gate wirings G1 to G8 connect the switch element of each pixel in arow direction, and are the wirings for turning ON and OFF each of theswitch elements T1-1 to T8-8. The driving circuit unit 121 a supplies adriving signal (pulse) to each of the gate wirings G1 to G8 so as todrive each of the switch elements T1-1 to T8-8 and drive each of thephotoelectric conversion elements S1-1 to S8-8. The signal wirings M1 toM8 are wirings for connecting the switch element of each pixel in acolumn direction and reading the electric signals (electric charges) ofthe photoelectric conversion elements S1-1 to S8-8 through the switchelements T1-1 to T8-8 to the readout circuit unit 121 b.

A switch RES is for resetting capacitors Cf1 to Cf8. A switch Gain is again selector switch of Amp of the readout circuit unit 121 b. The AmpsA1 to A8 are for amplifying the electric signals from the signal wiringsM1 to M8. A Vref wiring is a wiring for supplying a reference powersource from the power source circuit unit 121 c to the Amps A1 to A8.Capacitors CL1 to CL 8 are sample-hold capacitors for temporarilystoring the electric signals amplified by the Amps A1 to A8. A switchSMPL is for performing a sample hold. Switches AVE1 and AVE2 areswitches for subjecting the electric signals sample-held to a pixeladdition (averaging out). AD converters ADC1 to ADC8 are for convertingthe electric signals (analogue signals) sample-held by the sample-holdcapacitors CL1 to CL8 into digital signals. The digital signals afterthis AD conversion, for example, are output to the image processing unit105 and the like, and are subjected to the predetermined processing suchas the image processing, and after that, the display and storage of theprocessed image data are performed.

Next, information stored in the calibration table memory 106 will bedescribed. FIG. 3 is a view showing one example of a calibration tableused for the x-ray imaging system according the first embodiment. Thecalibration table shown in FIG. 3 is stored in the calibration tablememory 106. Here, the calibration table means a table for settingradiographing conditions to the x-ray imaging apparatus 101 and thex-ray generator apparatus 102 when performing a calibration.Specifically, the calibration table memory 106 is specified in theirradiation conditions (irradiation mode, tube voltage, tube current,and irradiation time) in the x-ray generator apparatus 102 and thedriving conditions (gain and driving method) in the x-ray imagingapparatus 101 according to each operation mode. Here, the <gain>indicates an amplification factor of the Amps A1 to A8 of the readoutcircuit unit 121 b. Further, the <driving method> relates to the numberof additions when reading the electric signal of the unit pixel 100.

Further, in the present embodiment, as the driving conditions in thex-ray imaging apparatus 101, in addition to the gain and driving methodshown in FIG. 3, a mode in which the calibration table is formed byincluding the voltage applied to the photoelectric conversion elementand the voltage applied to the switch element can be also applied.

Here, the operation modes in the x-ray imaging system of the presentembodiment will be described.

In a still image radiographing mode, since only one sheet of image isradiographed, there is no need to quicken a frame rate, and a resolvingpower is required, and therefore, the addition driving of the unit pixelis not performed. Further, as shown in FIG. 3, a moving imagephotographing mode includes a total of three types, and each isdifferent in the number of additions of the unit pixel. Specifically,the moving image radiographing mode includes three modes of a firstmoving radiographing mode (one×one pixel addition: non-pixel addition),a second moving image radiographing mode (2×2 pixel addition), and athird moving image radiographing mode (4×4 pixel addition).

In the addition processing of the unit pixel, since the signals of aplurality of unit pixels are read simultaneously, the frame rate becomesfast and the S/N becomes also high, but because the plurality of unitpixels are put into one pixel and output, the resolving power isreduced. Hence, to which item from among the frame rate, S/N, andresolving power, the engineer 110 gives priority to radiograph dependingon the condition and the like of the object 116 is selected by using theoperator interface 108. In the calibration table of the presentembodiment, three tube voltage modes of low tube voltage/medium tubevoltage/high tube voltage are specified every four radiographing modesshown in FIG. 3. The image processing unit 105 extracts an image forgain correction in the tube voltage closest to a tube voltage havingactually radiographed the object 116 from the image memory for gaincorrection 107, and performs a gain correction of the object image byusing the extracted image for gain correction.

Next, by using the timing chart shown in FIGS. 4 to 6, the operation ofthe x-ray imaging system according to the present embodiment will bedescribed.

FIG. 4 is a timing chart showing a driving method in the non-pixeladdition of the x-ray imaging system according to the first embodiment.Based on this timing chart, the operations of the conversion circuitunit 120, driving circuit unit 121 a and readout circuit unit 121 b asshown in FIGS. 2A and 2B will be described.

First, the operation in a photoelectric conversion period (x-rayirradiation period) will be described.

In a state in which all the switch elements are turned off, when thex-ray is irradiated pulse-wise from the x-ray generator apparatus 102,an x-ray or a light converted in wavelength from the x-ray is irradiatedto each photoelectric conversion element. Electric signals (electriccharges) according to the quantity of the x-ray or light are accumulatedin each photoelectric conversion element.

At this time, when the above described wavelength converter 118 forconverting the x-ray into a visible light is used, a member for guidingthe visible light corresponding to the amount of the x-ray to thephotoelectric conversion element side is used, or alternatively, thewavelength converter 118 may be disposed extremely close to thephotoelectric conversion element. Incidentally, even after the x-raybecomes non-irradiative, each photoelectric conversion element holds thephotoelectrically converted electric signal (electric charge).

Next, the operation during the readout period will be described. Thereadout operation is performed in order of the photoelectric conversionelements S1-1 to S1-8 of the first line, the photoelectric conversionelements S2-1 to S2-8 of the second line, and the photoelectricconversion elements S3-1 to S3-8 of the third line, and this readout isperformed up to the photoelectric conversion elements S8-1 to S8-8 ofthe eighth line.

First, to read out the electric signals (electric charges) accumulatedin the photoelectric conversion elements S1-1 to S1-8 of the first line,the gate wiring G1 connected to the switch elements T1-1 to T1-8 of thefirst line from the driving circuit unit 121 a is given a driving signal(pulse). At this time, the driving circuit unit 121 a, based on acontrol from the radiographing controller 122, outputs the drivingsignal to the gate wiring G1. As a result, the switch elements T1-1 toT1-8 of the first line are put into a turned on state, and the electricsignals based on the electric charges accumulated in the photoelectricconversion elements S1-1 to S1-8 of the first line are transferredthrough the signal wirings M1 to M8.

The electric signals transferred to the signal wirings M1 to M8 areamplified by the Amps A1 to A8 according to capacitance of thecapacitors Cf1 to Cf8. The amplified electric signals are sample-held inthe capacitors CL-1 to CL8 by SMPL signals based on a control from theradiographing controller 122. After that, the electric signalssample-held by the capacitors CL1 to CL8 are AD-converted by the ADconverters AD1 to AD8, and are output to the image processing unit 105and the like as digital data.

Similarly to the readout operation of the photoelectric conversionelements S1-1 to S1-8 of the first line, the readout operation of thephotoelectric conversion elements S2-1 to S2-8 of the second line andthe readout operation of the photoelectric conversion elements S3-1 toS3-8 of the third line are performed in order, and subsequently, thereadout operations up to the fourth line to the eighth line areperformed.

In this manner, the x-ray is converted into the visible light by usingthe wavelength converter 118, and the visible light is converted intothe electric charge by each photoelectric conversion element, and thex-ray information is readout as the electric signal, so that theinformation on the object 116 can be obtained.

Next, by using FIG. 5, the driving method of the 2×2 pixel addition willbe described.

FIG. 5 is a timing chart showing the driving method in the 2×2 pixeladdition of the x-ray imaging system according to the first embodiment.

The driving in the 2×2 pixel addition, as compared to the case where thepixel addition shown in FIG. 4 is not performed, is different in thenumber of gate wirings for turning ON/OFF simultaneously. As shown inFIG. 4, in the driving of the non-pixel addition, while the gate wiringsare turned ON/OFF in order of G1, G2, G3 . . . , in the driving of the2×2 pixel addition, each group of G1 and G2, G3 and G4, G5 and G6, andG7 and G8 is turned ON/OFF simultaneously.

When the gate wirings G1 and G2 are simultaneously turned ON byperforming the driving of such 2×2 pixel addition, the switch elementsT1-1 to T2-8 are simultaneously opened, and for example, a sum of theelectric signals (electric signals two times the non-pixel addition) ofthe photoelectric conversion elements S1-1 and S2-1 is accumulated inthe capacitor Cf1. Further, in the driving of the 2×2 pixel addition,since the readout time becomes 1/2 as compared to the case where thepixel addition is not performed, the frame rate becomes twofold.

Further, in the driving of the 2×2 pixel addition, the pixel addition isperformed also in the direction to the signal wiring. Specifically, bythe input of the AVE1 signal based on a control from the radiographingcontroller 122 after being sample-held in the capacitors CL1 to CL8,each capacitance of the capacitors CL1 and CL2, CL3 and CL4, CL5 andCL6, and CL7 and CL8 are combined, and the sample-held signals areaveraged out. As a result, the electric signals of the 2×2 pixels areadded into one pixel, and are output as a plural pixel. In this case,while the size of the electric signal does not change, the noise becomes1/(√2)times, so that the S/N becomes (√2)times.

Next, by using FIG. 6, the driving method of the 4×4 pixel addition willbe described.

FIG. 6 is a timing chart showing a driving method in the 4×4 pixeladdition in the x-ray imaging system according to the first embodiment.

In the driving in the 2×2 pixel addition, while the gate wirings areturned ON/OFF two pieces simultaneously, in the driving in the 4×4 pixeladdition, the gate wirings are turned ON/OFF four pieces simultaneouslyso as to perform the readout. Hence, fourfold signal is output. Further,as compared to the driving in the 2×2 pixel addition, the readout periodis also shortened by 1/4, and the frame rate becomes fourfold.

With respect to the pixel addition in the direction to the signalwiring, by the pulse input of the AVE1 signal and the AVE2 signal basedon a control from the radiographing controller 122 after beingsample-held in the capacitors CL1 to CL8, each capacitance of thecapacitors CL1-CL4 and the capacitors CL5 to CL8 is combined. As aresult, the electric signals sample-held in each of the capacitors CL1to CL8 are averaged out, and the averaged analogue signals areAD-converted, and the electrical signals of the 4×4 pixels are addedinto one pixel, and are output as a plural pixel.

As described above, by the driving of the non-pixel addition, 2×2 pixeladdition, and 4×4 pixel addition, the S/N can be made high and the framerate can be made fast.

Next, the radiographing of the image for gain correction, which is thecharacteristic of the present invention, will be described.

In the present embodiment, to obtain the radiographed image having highS/N and no artifact, the image for gain correction is radiographed everyradiographing mode. In the present embodiment, as shown in FIG. 3, atotal of four operation modes of one still image radiographing mode andthree moving image radiographing modes are set. In the presentembodiment, as shown in FIG. 3, the images for gain correction in threetube voltages different in the low tube voltage, medium tube voltage,and high tube voltage every operation mode are radiographed. Hence, inthe present embodiment, the images for gain correction of 12 sheets=fourradiographing modes×three tube voltages are radiographed.

Further, even when the same x-ray is irradiated, the signal amountoutput from the photoelectric conversion circuit unit 120 is differentevery radiographing mode. For example, in the driving in the 2×2 pixeladdition which is a second moving image radiographing mode, the additionprocessing in the direction to the gate wiring is performed, whereas, inthe direction to signal wiring, because of the averaging out, thesignals two times that of the non-pixel addition mode are output. Hence,when the same x-ray amount as the first moving image radiographing mode(one×one pixel addition) is irradiated at the time of the second movingimage radiographing mode (2×2 pixel addition), dynamic ranges of theAmps and AD converters of the readout circuit unit 121 b sometimes endup saturating.

Further, in the moving image radiographing mode and the still imageradiographing mode, the gains of the Amps A1 to A8 of the readoutcircuit unit 121 b are different. The switching over of the gains atthis time is performed such that, by the input of the gain signals basedon a control of the radiographing controller 122, the switch Gains shownin FIGS. 2A and 2B are operated, thereby switching over the integralcapacities (Cg and Cf) of the Amps A1 to A8 of the readout circuit unit121 b.

Since the output of each of the Amps A1 to A8 of the readout circuitunit 121 b is the output=1/integral capacity, smaller the integralcapacity is, higher the gain becomes, and higher level the output signalis. In the still image radiographing, since one sheet only of image isradiographed, no problem is caused even if the x-ray amount to beirradiated is slightly larger, whereas, in the case of the moving imageradiographing, the time to irradiate the x-ray is long, and therefore,the x-ray amount to be irradiated per one image sheet is required to belimited to the minimum. Hence, to obtain the electric signals from theleast x-ray amount, readout of the high again is performed.

In this manner, the moving image radiographing mode and the still imageradiographing mode, the number of additions of the unit pixel, and theelectric signals output from the photoelectric conversion circuit 120 bythe tube voltage and the like of the x-ray tube bulb 113 are different.Hence, in consideration of the dynamic range of each of the Amps A1 toA8 and AD converters AD1 to AD8 of the readout circuit unit 121 b, theconditions of the x-ray radiographing are required to be decided.However, to radiograph the image for gain correction, it is difficultfor the engineer 110 to decide its condition one by one every operationmode and perform the setting.

Hence, in the present embodiment, the calibration table set with theirradiation conditions of the x-ray and the driving conditions of thex-ray imaging apparatus per each operation mode is stored in thecalibration table memory 106 in advance. Based on the data of thiscalibration table, the radiographing controller 122 allows the x-rayimaging apparatus 101 and the x-ray generator apparatus 102 to operate,and therefore, the engineer 110 can perform the calibration only bydepressing an exposure button (not shown) every operation mode. Here, inthe present embodiment, for example, the operator interface 108comprises the exposure button (not shown).

Next, the acquisition processing of the image for gain correction willbe described.

FIG. 7 is a flowchart showing the acquisition processing of the imagefor gain correction of the x-ray imaging system according to the firstembodiment. That is, FIG. 7 is a flowchart showing a procedure in thecalibration.

First, when starting the calibration, the engineer 110 operates theoperator interface 108, and performs an alignment between the x-rayimaging apparatus 101 and the x-ray generator apparatus 102 (step S101).Specifically, the engineer 110 performs the alignment in such a mannerthat an irradiation center of the x-ray by the x-ray tube bulb 113 ispositioned at the center of the x-ray imaging apparatus 101.Subsequently, the engineer 110 instructs the start of the calibrationfrom the operator interface 108 (step S102).

The radiographing controller 122 having received the start of thecalibration from the operator interface 108 reads the calibration tablestored in the calibration table memory 106 (step S103). In the presentembodiment, though a mode of storing the calibration table in adedicated memory 106 is shown, for example, the mode may be such thatthe table is stored in the external storage unit 111 with no dedicatedmemory 106 provided.

Subsequently, the radiographing controller 122, according to the orderof the calibration table, first performs a processing to start theradiographing of the image for gain correction in the case where thex-ray tube bulb 113 is at the low tube voltage (50 kVp) in the stillimage radiographing mode shown in FIG. 3 (step S104). Here, whenradiographing the image for gain correction, the radiographing isperformed in a state in which no object 116 exists.

Subsequently, the radiographing controller 122 performs the setting ofthe irradiation conditions (irradiation mode, tube voltage, tube currentand irradiation time) of the x-ray shown in the calibration table ofFIG. 3 for the x-ray generator apparatus 102 (step S105). Specifically,at step S105, the irradiation conditions are set for the x-ray generatorapparatus 102 to the effect that the irradiation mode is <general>, thetube voltage of the x-ray tube bulb 113 is <50 (kVp)>, the tube currentis <125 (mA)>, and the irradiation time is <50 (ms)>.

As described above, in the present embodiment, as the setting of theirradiation conditions of the x-ray for the x-ray generator apparatus102, the tube voltage of the x-ray tube bulb 113, tube current,irradiation time and irradiation mode of the x-ray are set. Further,other than these conditions, as the setting of the irradiationconditions of the x-ray for the x-ray generator apparatus 102, an x-rayaperture 114 can be also worked together.

Subsequently, the radiographing controller 122 performs the setting ofthe driving conditions (gain and driving method) shown in thecalibration table of FIG. 3 for the x-ray radiographing apparatus 101(step S106). Specifically, at step S106, the driving conditions are setfor the x-ray imaging apparatus 101 to the effect that the gain is <1>and the driving method is the <still image driving>.

As described above, in the present embodiment, as the setting of thedriving conditions for the x-ray imaging apparatus 101, the drivingmethod (driving timing) and the gain are set. The setting conditions ofthe x-ray imaging apparatus 101 and the x-ray generator apparatus 102stored in the calibration table are decided when the x-ray imagingapparatus 101 or the x-ray generator apparatus 102 is installed in thehospital, and after installing, the calibration is periodicallyperformed according to the calibration table.

Subsequently, the radiographing controller 122 sets the radiographingconditions in the x-ray imaging apparatus 101 and the x-ray generatorapparatus 102, and after that, drives the x-ray imaging apparatus 101and the x-ray generator apparatus 102 so as to prepare for radiographing(step S107), and waits for the depression of the exposure button (notshown) by the engineer 110.

When the exposure button (not illustrated) is depressed by the engineer110 and the exposure button is turned on, the radiographing controller122 detects this (step S108).

Subsequently, the radiographing controller 122, based on theradiographing conditions set at step S105 and S106, allows the x-rayimaging apparatus 101 and the x-ray generator apparatus 102 to bedriven, and performs the capturing of the radiographed image (stepS109). Specifically, under the irradiation conditions set at step S105,the x-ray is irradiated from the x-ray generator apparatus 102 to thex-ray imaging apparatus 101. In the x-ray imaging apparatus 101, thex-ray from the x-ray generator apparatus 102 is received by thephotoelectric conversion circuit unit 120, and based on the drivingconditions set at step S106, the image data radiographed by the drivingcircuit unit 121 a and the readout circuit unit 121 b is read by thecontrol apparatus 109. This image data read by the control apparatus 109is the image data for gain correction used for the gain correctionprocessing.

Subsequently, the image processing unit 105, based on a control from theradiographing controller 122, performs a basic processing such as anoffset correction for the image data for gain correction read from thex-ray imaging apparatus 101 (step S110). Next, the image processing unit105, based on a control from the radiographing controller 122, holds theimage data for gain correction which is subjected to the imageprocessing in the image memory 107 for gain correction (step S111).

By going through the processings of these steps S104 to S111, theacquisition processing of the image for gain correction is performed inthe case where the x-ray tube bulb 113 is at the low tube voltage (50kVp).

Subsequently, the radiographing controller 122, by the still imageradiographing mode shown in FIG. 3 according to the order of thecalibration table, performs a processing of starting the radiographingof the image for gain correction in the case where the x-ray tube bulb113 is at the medium tube voltage (80 kVp) (step S112). From thenonward, the radiographing controller 122 repeats the same processing asthe acquisition processing (steps S104 to s111) of the image for gaincorrection according to the order of the calibration table of FIG. 3 inthe case where the x-ray tube bulb 113 is at the low tube voltage, sothat the images for gain correction of the remaining eleven types shownin FIG. 3 can be obtained. As a result, the image data for gaincorrection every operation mode of a total twelve types shown in FIG. 3can be stored in the image memory 107 for gain correction.

In the first embodiment, though the image for gain correction isradiographed one sheet every operation mode, the images of n sheets areradiographed every operation mode, and the images of the n sheetssubjected to an averaging-out processing can be also applied as theimages for gain correction. In this manner, the images subjected to anaveraging-out processing are taken as the images for gain correction, sothat the correction images having a noise reduced to 1/(√n) and high inS/N can be obtained.

In this manner, when the acquisition processing of the image for gaincorrection shown in FIG. 7 is performed, the engineer 110 only performsthe operations of (1) alignment between the x-ray imaging apparatus 101and the x-ray generator apparatus 102 (step S101), (2) issuance of theinstruction to start the calibration from the operator interface 108(step S102), and (3) depression of an irradiation button (notillustrated) every operation mode (12 times) (step S108), and sincethere is no need to perform the setting of radiographing conditions forthe x-ray imaging apparatus 101 and the x-ray generator apparatus 102every operation mode, no error in the calibration arises, and moreover,the number of man-hours can be suppressed to the minimum.

Next, the actual object radiographing operation in the case where theobject 116 is disposed will be described.

FIG. 8 is a flowchart showing the processing in the radiographingoperation of the x-ray imaging system according to the first embodiment.

Before starting the object radiographing, the engineer 110 allows theobject 116 to stand up or lie down at the predetermined position betweenthe x-ray imaging apparatus 101 and the x-ray generator apparatus 102,and performs confirmation of the positional relationship between theobject 116 and the x-ray imaging apparatus 101 and confirmation of theangle of the object 116.

Subsequently, the engineer 110 selects an operation mode (radiographingmode) to perform the object radiographing from among a total of 12 typesof operation modes shown in FIG. 3 having performed the calibration byoperating the operator interface 108 (step S201). At this time, forexample, a mode may be adapted such the region to be radiographed andthe operation mode are kept associated, and the engineer 110 selects theregion to be radiographed, so that the radiographing mode is selected.

Subsequently, the radiographing controller 122, based on the operationmode selected at step S201, refers to the calibration table, and setsthe radiographing conditions in the x-ray imaging apparatus 101 and thex-ray generator apparatus 102 (step S202). Here, for example, at stepS201, consider the case where the operation mode in which the x-ray tubebulb 113 is at the <low tube voltage> in the <still image radiographingmode> is selected. In this case, the radiographing controller 122 setsthe irradiation conditions for the x-ray generator apparatus 102 to theeffect that the irradiation mode is <general>, the tube voltage of thex-ray tube bulb 113 is <50 (kVp)>, the tube current is <125 (mA)>, andthe irradiation time is <50 (ms)>. Further, the radiographing controller122 sets the driving conditions for the x-ray imaging apparatus 101 tothe effect that the gain is <1>, and the driving method is <still imagedriving>. The radiographing controller 122 drives the x-ray imagingapparatus 101 and the x-ray generator apparatus 102 so as to prepare forthe radiographing, and waits for the depression of the exposure button(not illustrated) by the engineer 110.

When the exposure button (not illustrated) is depressed by the engineer110 and the exposure button is turned on, the radiographing controller122 detects this (step S203).

Subsequently, the radiographing controller 122, based on theradiographing conditions set at step S202, drives the x-ray imagingapparatus 101 and the x-ray generator apparatus 102 so as to perform thecapturing of the radiographed image (S204). Specifically, the x-ray isirradiated from the x-ray generator apparatus 102 under the irradiationconditions set at step S202, and the x-ray having transmitted the object116 enters the x-ray imaging apparatus 101. At the x-ray imagingapparatus 101, the x-ray having transmitted the object 116 is receivedby the photoelectric conversion circuit unit 120, and based on thedriving conditions set at step S202, the object image data radiographedby the driving circuit unit 121 a and the readout circuit unit 121 b isread by the control apparatus 109.

Subsequently, the image processing unit 105, based on a control from theradiographing controller 122, performs a basic image processing such asan offset correction for the object image data read from the x-rayimaging apparatus 101 (step S205).

Subsequently, the image processing unit 105, based on a control from theradiographing controller 122, performs the gain correction for theobject image data processed at step S205 (step S206). Specifically, theimage processing unit 105, first, extracts the image data for gaincorrection radiographed under the same conditions as the operation modeselected at step S201 from among the image memory 107 for gaincorrection. The image processing unit 105 divides the object image databy the extracted image data for gain correction or the like, therebyperforming the gain correction. After that, the image processing unit105 further performs a defect correction processing, spatial filteringprocessing, gradation processing, scattered radiation correctionprocessing, spatial frequency processings of various types, and the likeas occasion demands and according to the image processing conditions.

Subsequently, the image processing unit 105, based on a control from theradiographing controller 122, displays the object image data subjectedto the image processing on a monitor (the operator interface 108 in thepresent embodiment) as the object image (step S207).

Here, in the case of the moving image radiographing, the x-ray ispulse-irradiated from the x-ray generator apparatus 102, and performsradiographing→readout→image processing→display renewal in real time.

As described above, by using the calibration table, the image for gaincorrection can be easily radiographed every operation mode. By using thesame image for gain correction radiographed by the same operation modeat the radiographing time of the object image, the gain correction ofthe object image is performed, so that the object image having a highgrade quality and no artifact can be obtained.

(Second Embodiment)

Next, a second embodiment of the present invention will be described.

The configuration of a radiation imaging system according to the secondembodiment is the same as the radiation imaging system according to thefirst embodiment shown in FIGS. 1 and 2. Further, the processing in theradiographing operation of the radiation imaging system according to thesecond embodiment is the same as the processing in the radiographingoperation of the radiation imaging system according to the firstembodiment shown in FIG. 8. In the radiation imaging system according tothe second embodiment, since the difference with the radiation imagingsystem according to the first embodiment is only about an acquisitionprocessing of an image for gain correction, the description thereof onlywill be made in the following.

FIG. 9 is a flowchart showing the acquisition processing of the imagefor gain correction of the x-ray imaging system according to the secondembodiment. That is, FIG. 9 is a flowchart showing the procedure in acalibration.

In the first embodiment, the mode was such that the calibration table isread, and radiographing conditions are set in the x-ray generatorapparatus 102 and the x-ray imaging apparatus 101, and the exposurebutton (not illustrated) is depressed by the engineer 110 everyoperation mode, so that the radiographing of the image for gaincorrection is performed. On the other hand, in the second embodiment,the x-ray is automatically irradiated without the exposure button (notillustrated) depressed by the engineer 110, thereby to perform theradiographing of the image for gain correction.

Hereinafter, a description will be made based on the flowchart shown inFIG. 9.

First, similarly to the first embodiment, when starting the calibration,the engineer 110 operates an operator interface 108 and performs analignment between the x-ray imaging apparatus 101 and the x-raygenerator apparatus 102 (step S301). Subsequently, the engineer 110instructs the start of an automatic calibration from the operatorinterface 108 (step S302).

A radiographing controller 122 having received the start of theautomatic calibration from the operator interface 108 reads acalibration table stored in a calibration table memory 106 (step S303).

Subsequently, the radiographing controller 122, according to the orderof the calibration table, first, performs a processing for starting theradiographing of the image for gain correction in the case where anx-ray tube bulb 113 is at a low tube voltage (50 kVp) by a still imageradiographing mode shown in FIG. 3 (step S304). Here, when theradiographing of the image for gain correction is performed, it isperformed in a state in which the object 116 does not exist.

Subsequently, the radiographing controller 122 performs the setting ofthe irradiation conditions (irradiation mode, tube voltage, tubecurrent, and irradiation time) of the x-ray shown in the calibrationtable of FIG. 3 for the x-ray generator apparatus 102 (step S305).

Subsequently, the radiographing controller 122 performs the setting ofthe driving conditions (gain and driving method) shown in thecalibration table of FIG. 3 for the x-ray imaging apparatus 101 (stepS306).

Subsequently, the radiographing controller 122 sets the radiographingconditions for the x-ray imaging apparatus 101 and the x-ray generatorapparatus 102, and after that, drives the x-ray imaging apparatus 101and the x-ray generator apparatus 102 so as to prepare for theradiographing (step S307).

After having completed the radiographing preparation of step S307, theradiographing controller 122, based on the irradiation conditions set atstep S305, allows the x-ray generator apparatus 102 to be driven andallows the x-ray to be automatically irradiated from the x-ray generatorapparatus 102 (step S308).

Subsequently, the radiographing apparatus 122, based on the drivingconditions set at step S306, allows the x-ray imaging apparatus 101 tobe driven, and performs the capturing of the radiographed image (stepS309). Specifically, in the x-ray imaging apparatus 101, first, thelight converted by a wavelength converter 118 according to the x-rayfrom the x-ray generator apparatus 102 is received by a conversioncircuit unit 120. Based on the driving conditions set at step S306, adriving circuit unit 121 a and a readout circuit unit 121 b are driven,so that the radiographing is performed, and the radiographed image datais read by a controller apparatus 109. This image data read by thecontroller apparatus 109 is an image data for gain correction used for again correction processing.

Subsequently, the image processing unit 105, based on a control from theradiographing controller 122, performs a basic image processing such asan offset correction for the image data for gain correction read fromthe x-ray imaging apparatus 101 (step S310). Subsequently, the imageprocessing unit 105, based on a control from the radiographing controlunit 122, stores the image data for gain correction subjected to theimage processing in the image memory 107 for gain correction (stepS311).

By going through the processings of these steps S304 to S311, theacquisition processing of the image for gain correction is performed inthe case where the x-ray tube bulb 113 is at the low tube voltage (50kVp).

Subsequently, the radiographing controller 122, according to the orderof the calibration table, performs a processing for starting theradiographing of the image for gain correction by a still imageradiographing mode shown in FIG. 3 in the case where the x-ray tube bulb113 is at the medium tube voltage (80 kVp) (step S312). From thenonward, according to the order of the calibration table of FIG. 3, theradiographing controller 122 repeats the same processing as theacquisition processing (steps S304 to S311) of the image for gaincorrection in the case where the x-ray tube bulb 113 is at the low tubevoltage, so that the images for gain correction of the remaining eleventypes shown in FIG. 3 can be obtained. As a result, the image data forgain correction every operation mode of a total twelve types shown inFIG. 3 can be stored in the image memory 107 for gain correction.

In general, the exposure of the x-ray is performed by the x-rayirradiation for the irradiation time set by the logical product of anexposure request signal from the radiographing controller (controllerapparatus) and an exposure button signal, whereas, in the secondembodiment, at the calibration time only, the x-ray is irradiated by theexposure request signal only from the radiographing controller 122. Byso doing, when the calibration is once started, the engineer 110 needsnot to do anything until the completion of the calibration. Hence,according to the second embodiment, the number of operation processsteps can be reduced much more than the calibration operation in thefirst embodiment.

(Third Embodiment)

Next, a third embodiment of the present invention will be described.

In a radiation imaging system according to the third embodiment, thedifference with the radiation imaging system of the first embodiment isonly about information on a calibration table stored in a calibrationtable memory 106, and the description thereof only will be made in thefollowing.

FIG. 10 is a view showing one example of the calibration table used forthe x-ray imaging system according to the third embodiment.

The calibration table in the third embodiment shown in FIG. 10, ascompared to that of the first embodiment shown in FIG. 3, is read as thedriving conditions of the x-ray imaging apparatus 101, and is added witha cut off frequency (fc) of a low pass filter in the Amp of a readoutcircuit unit 121 b.

Further, in the present embodiment, as the driving conditions in thex-ray imaging apparatus 101, other than those shown in FIG. 10, the modeforming a calibration table further including the voltage applied to thephotoelectric conversion element and the voltage applied to the switchelement can be applied.

In the still image radiographing mode, since the read time is slow, thecut off frequency fc is made low with the noise reduced small as shownin FIG. 10, and further, in the moving image radiographing mode, sincethe read time is fast, the cut off frequency fc is made high as shown inFIG. 10. Further, in addition to the time constant of the low passfilter, the bias conditions of the photoelectric conversion element arechanged so as to change the sensitivity characteristics of thephotoelectric conversion element, and the ON voltage of the switchelement is changed so as to change the ON resistance of the switchelement, so that the suitable gain correction can be performed at thestill image radiographing time and the moving image radiographing time.

Each unit of FIGS. 1 and 2 comprising the radiation imaging systemaccording to the above described each embodiment and each step of FIGS.7 to 9 showing the driving method of the radiation imaging system can berealized by operating the program stored in the RAM and ROM or the like.This program and a computer readable storage medium recorded with thisprogram are included in the present invention.

Specifically, the program, for example, is recorded in the storagemedium such as CD-ROM or supplied to a computer through various transfermediums. As the storage medium storing the program, in addition toCD-ROM, a flexible disc, hard disc, magnetic tape, magneto-optic disc,non-volatile memory card, and the like can be used. On the other hand,as the transfer medium of the program, a communication medium in thecomputer network (LAN, WAN such as Internet, wireless communicationnetwork, and the like) system for propagating and supplying the programinformation as a carrier wave can be used. Further, as the communicationmedium at this time, a wire circuit or a radio circuit such as anoptical fiber can be cited.

Further, not only in the case where a computer executes a providedprogram so that the functions of the radiation imaging system accordingto each embodiment are not only realized, but also in the case where thefunctions of the radiation imaging system according to each embodimentare realized by the program in association with the OS (Operatingsystem) operated inside the computer or other application soft and thelike and as well as the case where all or a part of processings of theprovided program are executed by the function expanding board or thefunction expanding unit so that the functions of the radiation imagingsystem according to each embodiment are realized, such program is alsoincluded in the present invention.

The present invention relates to the radiation imaging system forradiographing a radiation image of the object and its driving method,and in particular, it is suitably used for the radiation imaging systemused for the diagnosis inside a hospital and the radiation imagingsystem used as a non-destructive inspection device for industrialpurpose.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1. A radiation imaging system comprising: a radiation imaging unit forperforming radiographing using radiation irradiated from a radiationgenerator that generates the radiation; a table storing unit for storinga table set with radiation conditions of the radiation of the radiationgenerator for an operation mode of a plurality of operation modes; aselecting unit for selecting an operation mode for performingradiographing from the plurality of operation modes; an image storingunit for storing image data of an image for gain correction obtainedbased on the radiation conditions set with the table in a state in whichan object is not present to be radiographed and in which radiation isirradiated to said radiation imaging unit for the operation mode of theplurality of operation modes; and an image processing unit configured toperform a gain correction processing of object image data, wherein saidimage processing unit performs the gain correction processing of theobject image data obtained based on the radiation condition set in thetable of the operation mode selected by the selecting unit in a state inwhich the object is present to be radiographed using a correspondingimage for gain correction extracted from said image storing unit basedon the operation mode selected by the selecting unit.
 2. The radiationimaging system according to claim 1, wherein said radiation imaging unitcomprises a conversion unit having a plurality of pixels in a twodimensional matrix pattern, wherein each pixel comprises a conversionelement for converting the radiation into an electric signal and aswitch element for transferring the electric signal of said conversionelement, and a readout unit for reading the electric signal from theconversion unit.
 3. The radiation imaging system according to claim 2,further comprising a control unit driving the radiation imaging unitbased on driving conditions set in the table of the operation modeselected by the selecting unit.
 4. The radiation imaging systemaccording to claim 3, wherein the driving conditions of said radiationimaging unit set in the table include at least one of: an amplificationfactor of the electric signal in said readout unit, a number ofadditions in the electric signal of said pixel when reading the electricsignal from said conversion unit, voltage applied to said conversionelement, voltage applied to said switch element, and the cutofffrequency of a low pass filter in said readout unit.
 5. The radiationimaging system according to claim 2, wherein said conversion elementincludes a photoelectric conversion element, and said photoelectricconversion element has amorphous silicon as its primary material.
 6. Theradiation imaging system according to claim 5, wherein saidphotoelectric conversion element includes a MIS-type photoelectricconversion element or a PIN-type photoelectric conversion element. 7.The radiation imaging system according to claim 5, further comprising awavelength converter for converting a wavelength of the radiation, andwherein said photoelectric conversion element receives incident lightproduced from the radiation by said wavelength converter.
 8. Theradiation imaging system according to claim 2, wherein said conversionelement has a function to absorb the radiation and directly convert theradiation into the electric signal, and said conversion element has asits primary material a material selected from the group consisting ofamorphous selenium, gallium arsenide, mercuric iodide, lead iodide, andcadmium telluride.